Magnetic and MO recording media are widely employed in various applications, particularly in the computer industry for data/information storage and retrieval purposes. A magnetic medium in, e.g., disk form, such as utilized in computer-related applications, comprises a non-magnetic substrate, for example, of glass, ceramic, glass-ceramic composite, polymer, metal or metal alloy, typically an aluminum (Al)-based alloy such as aluminum-magnesium (Al—Mg), having at least one major surface on which a layer stack comprising a plurality of thin film layers constituting the medium are sequentially deposited. In the case of longitudinal type magnetic recording media, such layers may include, in sequence from the substrate deposition surface, a plating layer, e.g., of amorphous nickel-phosphorus (Ni—P), a polycrystalline underlayer, typically of chromium (Cr) or a Cr-based alloy such as chromium-vanadium (Cr—V), a longitudinally oriented magnetic layer, e.g., of a cobalt (Co)-based alloy, and a protective overcoat layer, typically of a carbon (C)-based material, such as diamond-like carbon (DLC), having good mechanical (i.e., tribological) and corrosion resistance properties. Perpendicular type magnetic recording media typically comprise, in sequence from the surface of a non-magnetic substrate, an underlayer of a magnetically soft material, at least one non-magnetic interlayer or intermediate layer, a vertically (i.e., perpendicularly) oriented recording layer of a magnetically hard material, and a protective overcoat layer.
A similar situation exists with magneto-optical (MO) media, wherein a layer stack is formed which comprises a reflective layer, typically of a metal or metal alloy, one or more rare-earth thermo-magnetic (RE-TM) alloy layers, one or more dielectric layers, and a protective overcoat layer, for functioning as reflective, transparent, writing, writing assist, and read-out layers, etc.
According to conventional manufacturing technology, a majority (if not all) of the above-described layers constituting multi-layer longitudinal and perpendicular magnetic media, as well as MO recording media, are deposited by means of cathode sputtering processing. For example, the magnetic recording layers are typically fabricated by sputter depositing a Co-based alloy film, wherein the alloying elements are selected to promote desired magnetic and microstructural properties. In the case of longitudinal-type magnetic disk recording media, metallic and metalloidal elements, such as, for example, Cr, Pt, Ta, B, and combinations thereof, have been found to be effective. Similar alloying elements have been found to be useful in the case of perpendicular-type magnetic disk recording media, and in addition, reactive sputter deposition of the Co-based alloys in an oxygen (O2)-containing atmosphere has been found to be especially effective in controlling (i.e., limiting) exchange coupling between adjacent magnetic grains.
In a typical reactive sputtering process utilized for formation of perpendicular-type magnetic recording media, O2 gas is mixed with an inert sputtering gas, e.g., Ar, and is consumed by the depositing Co-based alloy magnetic film. Due to the high reactivity of O2 with metals, and since only partial oxidation of the depositing Co-based alloy magnetic film is desired, the degree of oxidation as a function of the location or position on the substrate (i.e., disk) surface tends to exhibit wide variation depending upon the process conditions, including, inter alia, O2 injection geometry, gas pumping (i.e., evacuation) geometry, gas flow rate, and film deposition rate.
FIG. 1 is a simplified, schematic, perspective view of a portion of a conventional reactive sputtering apparatus which may be utilized for performing reactive sputtering of magnetic thin films as part of the manufacturing process of disk-shaped magnetic recording media. As illustrated, the apparatus comprises a vacuum chamber equipped with an opening for connection to a pumping means for evacuating the interior of the chamber; at least one, preferably a pair of facing sputtering targets or sources of conventional type, e.g., a pair of magnetron sputtering guns; a means for positioning a substrate/workpiece in the space between the pair of facing sputtering sources, illustratively a disk-shaped substrate for a magnetic recording medium, for receipt of sputtered particle flux therefrom on both substrate surfaces; and a gas injector having a gas inlet portion extending outside the chamber for connection to a source of a gas, and a gas outlet portion within the chamber, for injecting gas, e.g., a reactive gas, in the space between the pair of facing sputtering sources. Illustratively, the gas injector is “wishbone”-shaped, and comprises a linearly elongated, tubular inlet portion having a first, gas inlet end, and a second end, with a pair of arcuately-shaped, tubular gas outlet portions extending from the second end, comprising a plurality of spaced-apart gas outlet orifices.
One-disk-at-a-time sputtering apparatus for the hard disk manufacturing industry, e.g., the Intevac MDP-250 (Intevac Co., Santa Clara, Calif.), typically employ gas injection means with design criteria, e.g., geometries, which are poorly suited to the high film uniformity requirements of the hard disk industry, particularly with respect to the special problems presented by reactive sputtering in atmospheres containing O2. For example, FIG. 2(B) is a graph illustrating the circumferential variation of S* for magnetic disks fabricated by means of “top-center” O2/Ar injection (relative to the disk) utilizing the “wishbone” style gas injector of the apparatus of FIG. 2(A), whereas FIG. 2(C) is a graph illustrating the circumferential variation of S* for magnetic disks fabricated by means of “bottom-side” O2/Ar injection utilizing the apparatus of FIG. 2(A), which apparatus comprises at least one conventional sputtering source for forming a film on at least one surface of the vertically positioned, dual-sided, disk-shaped magnetic disk substrate (which at least one conventional sputtering source is not shown in the figure for illustrative simplicity). Herein, the parameter S*=1−(dH/dM)Hc(Mr/Hc), and is closely related to the slope of the perpendicular M-H hysteresis loop at the coercive field. S* is a sensitive measure of the oxygen content of the oxide content of the perpendicular magnetic recording film. As the oxide content of the magnetic film increases, the exchange coupling between adjacent magnetic grains decreases, the hysteresis slope decreases, and S* decreases.
Specifically, it is seen from FIG. 2(B) that in the case of “top-center” O2/Ar injection, that S* is highest at the bottom of the disk (i.e., at 180°), indicating that the bottom of the disk is oxide-poor, relative to the disk top and sides (i.e., 0, 90, and 270°). By contrast, it is seen from FIG. 2(C) that in the case of “bottom-side” O2/Ar injection, that S* is lowest, i.e., the oxide content is highest, at the 90° position, corresponding to the region of the disk directly above the O2/Ar injection port.
A typical manufacturing specification for S* is in the range 0.30–0.50, with a tolerance of ±0.05, and nearly all of the magnetic films of FIGS. 2(B) and 2(C) are seen to exceed the specified tolerance for oxide content. However, the results of FIGS. 2(B) and 2(C) demonstrate that variation, e.g., asymmetry, of oxide content of the deposited magnetic films, as inferred from the values of the parameter S*, can be correlated with the O2/Ar injection geometry of the sputtering apparatus. In general, the oxide content is highest in the region of the disk surface which is closest to the point of O2/Ar injection. For the same sputtering chamber and pumping (evacuation) hardware, disks can be manufactured in which the magnetic recording layer is oxide rich at the top, bottom, or side(s), depending upon the geometry of the O2/Ar injection system, suggesting that the variation in oxide content of the magnetic recording layer (as reflected in the value of S*) can be reduced by proper design of the injection geometry/system.
In view of the foregoing, there exists a clear need for improved means and methodology for fabricating, by reactive sputtering techniques and at deposition rates consistent with the throughput requirements of automated manufacturing processing, thin films having a specified, typically minimal, compositional variation over the substrate surface, of a film constituent supplied via reactive gas injection to the sputtering atmosphere. More specifically, there exists a need for improved means and methodology for overcoming the above-described drawbacks and disadvantages associated with reactive sputtering processing for the manufacture of hard disk magnetic and MO recording media, notably oxide content variation over the disk surface which exceeds specified manufacturing tolerances.
The present invention addresses and solves the problems, disadvantages, and drawbacks described supra in connection with conventional means and methodology for performing reactive sputtering, e.g., of oxide-containing perpendicular magnetic recording layers, while maintaining full compatibility with all aspects of conventional automated manufacturing technology for hard disk magnetic and MO recording media. Further, the means and methodology afforded by the present invention enjoy diverse utility in the manufacture of all manner of devices and products requiring formation of high compositional uniformity thin films by means of reactive sputtering processing.